Motor Unit Territory in Different Human Muscles

Abstract B uchthal , P., I?. E rminio and P. R osekfalck . Motor unit territory in different human muscles. Acta physiol. scand . 1959. 45 . 72–47. — The spread of action potentials from motor units of different human muscles was studied by means of a twelve lead multielectrode. The occurrence of a positive‐negative deflection in the potential of less than 0.2 msec duration indicated the presence of active muscle fibres in the immediate vicinity of the recording lead. In this way the fibres of a motor unit were found to be confined to a circular area of 5–7 mm diameter for the muscles of the upper extremities and of 7–10 mm in the lower extremities. Such areas allow space for the fibres of 25 motor units each comprising 500–2,000 fibres. Within the same muscle or the same type of muscle the diameter of the motor unit territory varied by a factor of four. The maximum voltage within the motor unit increased linearly with the territory. The different average values of maximum voltage and territory in different muscles are interpreted in terms of differences in fibre concentration and total number of fibres per motor unit.